1. Field of the Invention
This invention relates to a process for preparing an immobilized microorganism or enzyme. More particularly, the invention relates to a process for preparing an immobilized microorganism or enzyme by using a mixture of an alginate and silica sol as an entrapping material.
2. Description of the Prior Art
An immobilizing method of microorganisms or enzymes by entrapping them with an alginate is known. This method causes little reduction of enzyme activity in the course of immobilizing operation as no heating is required and the gelation can be effected under the relatively mild conditions. This method is also safe in terms of food sanitation, and attempts are being made of the application of this technique to the food and pharmaceutical industries.
However, the alginate matrix gel is weak in mechanical strength and liable to deform and swell in comparison with the gel entrapped by using a polymeric compound such as acrylamide or polymethacrylate, so that great difficulties are involved in use of such alginate matrix gel as a packed bed type reactor which is generally used in the fermentation processes.
Methods are also known in which an inorganic substance, especially silica gel is used as immobilizing carrier for the gel containing a microorganism or enzyme. For instance, British Pat. No. 1,267,685 discloses a method in which hydrochloric acid is added to an aqueous solution of sodium silicate to prepare a silica sol having a pH of 1.6, then this sol is dialyzed to remove sodium chloride to obtain a stabilized silica sol, and after adjusting the pH to around 5-8, it is added with a microorganism or an enzyme and is converted to gel In the methods disclosed in Japanese Patent Application Kokai (Laid-Open) Nos. 120190/77 and 49392/79, an enzyme is adsorbed on colloidal silica, followed by the gelation thereof by the addition of a salt such as magnesium chloride, sodium carbonate or the like, and then the gel is subjected to freezing and thawing to obtain an pulverized immobilized gel.
These methods, however, had the following problems: much time is required for the preparation of silica sol used as base; the entrapping and immobilizing (gelation) operations are complicated; in use of these gels as a bioreactor, since such gels are an irregular or pulverized silica gel, no satisfactory packing effect is obtained when such gels are packed in a substrate reaction vessel, unless the gels are shaped into a form suited for said vessel
In order to eliminate these defects of the prior arts the present inventors have made more extensive studies and found that, when immobilizing a microorganism or enzyme, the use of a mixture of silica sol and an alginate as entrapping material enables prompt gelation with an ordinary gelling agent such as calcium chloride, aluminum chloride or the like, that the thus obtained gel containing the microorganism or the enzyme is extremely high in mechanical strength and has also strong resistance against the swelling because of a dual gel matrix structure comparising alginate gel and silica gel, and that, in the course of the immobilizing process, there takes place little reduction of enzyme activity. The present invention was achieved on the basis of these findings.